THE "BLIND ALLEY": ITS SIGNIFICANCE FOR
EVOLUTIONARY THEORY

Several scientists have apparently independently used the term "Blind Alley" to indicate that
major evolutionary change has ceased. The failure to observe speciation through selection
would indicate that obligatory sexual reproduction is incapable of producing progressive
evolution. Favoring this conclusion is the evidence that sex determination has independently
evolved and may be further correlated with the equally nonhomologous evolution of
contemporary gametic sources in the same animal groups. To incorporate these facts into a
meaningful theory demands the postulate of a presexual mode of reproduction which has been
suggested as identical with the first meiotic division. A hypothetical scenario for
macroevolution is presented.

In reviewing the evolution literature I was struck by the occurrence of the words "blind alley"
when various authors were discussing the evolutionary process. Once having identified the
cause of the blind alley I will follow that identification to its logical conclusions for our
understanding of the evolutionary process. Except for generic names, all italics have been added
by me.

I begin with Julian Huxley, one of a group of biologists including Mayr, Stebbins, Dobzhansky,
Wright and Simpson, who collectively instituted what they called the "Modern Synthesis." This
was, in effect, a consensus that evolution was essentially a neo-Darwinian process emphasizing
isolation and natural selection as creative forces in the molding of new life forms. In 1942
Huxley summarized the literature in his book appropriately titled "Evolution: The Modern
Synthesis". The so-called second edition, published in 1963 is actually the eighth printing of the
1942 text. On page 571, seven pages from the end, Huxley presents the following revealing
summary.

"Evolution is thus seen as a series of 'BlindAlleys'. Some are extremely short - those leading to
new genera and species that either remain stable or become extinct. Others are longer - the lines
of adaptive isolation within a group such as a class or subclass, which run for tens of millions of
years before coming up against their terminalblankwall. Others are still longer - the links that
in the past led to the development of the major phyla and their highest representatives; their
course is to be reckoned not in tens but in hundreds of millions of years. But all in the long run
have terminatedblindly. That of the echinoderms, for instance, reached its climax before the end
of the Mesozoic. For arthropods, represented by their highest group, the insects, the fullstop
seems to have come in the early Cenozoic. Even the ants and bees have made noadvance since
the Oligocene. For the birds the Miocene markedtheend; for the mammals, the
Pliocene"(HUXLEY 1963).

Huxley was not alone in these conclusions. Compare his views with those of the anti-Darwinian
paleontologist Robert Broom.

"In Eocene times - say between 50,000,000 and 30,000,000 years ago - small primitive mammals
rather suddenly gave rise to over a dozen very different orders - hoofed animals, odd-toed and
even-toed, elephants, carnivores, whales, rodents, bats, and monkeys. And after this there were
no more Orders of mammals ever evolved. There were great varieties of evolution in the Orders
that had appeared, but strangely enough Nature seemed incapable of forming any more new
Orders. What is equally remarkable, no new types of birds appear to have evolved in the last
30,000,000 years.
And most remarkable of all no new family of plants appears to have been evolved since the Eocene.
All major evolution has apparently come to an end. No new types of fishes, no new groups of
molluscs, or worms or starfishes, no new groups even of insects appear to have been evolved in
these latter 30,000,000 years" (BROOM 1951).

In an earlier work Broom was more explicit.

"There is, however, no doubt that evolution, so far as new groups are concerned, is at an end. That
a line of small generalized animals should have continued on till in Eocene times the Primates
originated and then ceased, and that except for specialisations of Eocene types there has been no
evolution in the last forty million years, and that the evolutionary clock has so completely run down
that it is very doubtful if a single new genus has appeared on earth in the last two million years, ..."
(BROOM 1933).

If one accepts the notion that macroevolution involves the formation of new kinds (genera) of living
things, then Broom is saying that all macroevolution ceased about two million years ago.

Now for the question: If, as these authors have indicated, major evolutionary change has indeed
ceased, what caused the process to come to a halt? In probing for an answer to this question I
consulted the opinions of one whose entire career involved the alteration of living things through
intensive artificial selection. While he does not use the term "Blind Alley" his conclusions imply
as much. From his autobiography Luther Burbank writes:

"There is a law of which I have not yet spoken that is useful to plant-breeders, as well as being a
limitation on them. It is called the 'law of the Reversion to the Average.'

I know from my experience that I can develop a plum half an inch long or one two and a half inches
long, with every possible length in between, but I am willing to admit that it is hopeless to try to get
a plum the size of a small pea, or one as big as a grape-fruit. I have daisies on my farms little larger
than my finger nail and some that measure six inches across, but I have non as big as a sunflower,
and never expect to have..... In short, there are limits to the developments possible, and these limits
follow a law" (BURBANK 1939).

Notice that Burbank does not even consider the question of speciation, rather he indicates with
confidence the limited extent within the species to which selection can go, essentially endorsing the
"Blind Alley" position. This I found rather remarkable since Burbank who was rather indifferent
towards Mendelism was an enthusiastic Darwinian (BURBANK 1931).

In this regard it is useful to recall the final words in Darwin's Origin of Species

"...endless forms most beautiful and most wondrous have been and are being evolved" (DARWIN
1896).

While no serious scientist questions the evidence that evolution has occurred, I hope the foregoing
may serve to justify asking whether or not it is still occurring. More specifically the question might
be phrased - can diploid sexually reproducing organisms undergo evolutionary change?

Darwin relied heavily on the variation observed among litter mates as the source of differences upon
which natural selection could act. With the rediscovery of Mendelian genetics in 1900 a great
impetus was given to Darwinism as a source of variation was finally revealed - the particulate gene.
A chief exponent of the new science of genetics was William Bateson, properly regarded as the
father of modern genetics. He coined the terms genetics, allelomorph, dominant, recessive and
Mendelism (DUNN 1965). His enthusiasm for Mendelism apparently extended to naming his son
Gregory when he was born in 1903. William Bateson was the earliest of my sources to use the term
"Blind Alley" and it is of interest to recognize how this comment came to be revealed.

In 1970 Arthur Koestler was completing research on his book "The Case of the Midwife Toad",
dealing with the career of the Lamarckian zoologist Paul Kammerer. His research included an
interview in June 1970 with Bateson's son Gregory, who offered the following recollection to
Koestler:

"By 1924, Bateson had come to realize, and told his son in confidence, 'that it was a mistake to have
committed his life to Mendelism, that it was a blindalley which would not throw any light on the
differentiation of species, nor on evolution in general'" (KOESTLER 1971).

Mendelism is of course the genetics associated with sexual reproduction. Bateson seems to be
saying the same thing that Burbank is saying, i.e. sexual forms are incapable of progressive change.
The obvious inference is that sexual reproduction is the "Blind Alley" of evolution. This
consideration forces another question. Is there another kind of genetics other than the Mendelian
variety? It is again useful to review the historical record.

The publication of R. B. Goldschmidt's "The Material Basis of Evolution" in 1940 marks a pivotal
point in the history of evolutionary thought. The text is in two sections, microevolution and
macroevolution. The first section on microevolution ends with this statement so reminiscent of
Bateson.

"Subspecies are actually, therefore, neither incipient species nor models for the origin of species.
They are more or less diversified blindalleys within the species. The decisive step in evolution, the
first step toward macroevolution, the step from one species to another, requires another evolutionary
method than that of sheer accumulation of micromutations" (GOLDSCHMIDT 1940).

This view was echoed a decade later by the systematist Petrunkevitch (PETRUNKEVITCH 1952).

"Without prejudice toward the studies on such animals as Drosophila, I believe that Goldschmidt
is right when he considers microevolution to be "a blind alley." All morphological evidence is in
favor of the assumption that macroevolutionary changes in Diptera were completed in the
comparatively distant past... At any rate it seems imperative that the methods for the production of
viable 'hopeful monsters' should be different from those employed for the production of
microevolutionary changes."

This call for a different evolutionary method should not be taken lightly. Like any new method two
aspects present themselves. The first is the method itself, the second, the means by which the
method has been implemented.

The other method to which Goldschmidt refers is the reorganization of existing genetic information
within the structure of the chromosome, a phenomenon loosely defined as position effect. In his
words

"... the fact remains that an unbiased analysis of a huge body of pertinent facts shows that
macroevolution is linked to chromosomal repatterning and that the latter is a method of producing
new organic reaction systems, a method which overcomes the great difficulties which the actual
facts raise for the neo-Darwinian conception as applied to macroevolution" (GOLDSCHMIDT
1940).

Unfortunately, Goldschmidt's views were not taken seriously at the time. First, the authors of the
"Modern Synthesis" were in the process of collectively stating their case for neo-Darwinism and
simply chose to ignore Goldschmidt's challenge. Second, molecular biology was emerging and
emphasis on the more traditional methods of cytogenetics was being overshadowed by interest in
the biochemistry of the nucleic acids and the emergence of the genic control of enzyme synthesis.

In any event we now know that Goldschmidt was prophetic indeed. Modern staining techniques
allow us to visualize chromosomal repatterning in a wide variety of life forms including the higher
primates which serve as a good example of what might be called position effect genetics.

While DNA hybridizing techniques (ANDREWS 1987) have revealed a surprising degree of
similarity between ourselves and our close relatives, the one clear distinction between us is that
foreseen by Goldschmidt. The 1982 paper by Yunis and Prakash (YUNIS and PRAKASH 1982)
illustrates that the major differences between ourselves, chimpanzees, gorillas and orang-utans are
evidenced as a repatterning of what seems to be otherwise identical blocks of euchromatic
chromosomal information. The notion of the chromosome as a field of reaction, considered radical
in Goldschmidt's day, is now accepted in the cytogenetics literature along with a renewed interest
in position effect genetics (LIMA-DE-FARIA 1983).

I now come to the question of how these new patterns came to be. If Burbank, Bateson and the
others are correct in their assessment of the limitations of sexual reproduction, then it follows that
macroevolution would be expected to involve a presexual mode of reproduction. It further follows
that sex-determinating mechanisms would be expected to evolve independently in various plant and
animal groups. Such is apparently the case. All known mammals have male heterogamety with the
familiar XY male and XX female. By contrast, all birds are the opposite with ZW females and ZZ
males. A similar dichotomy apparently evolved within the amphibia with most urodeles (newts and
salamanders) like birds and all anurans (frogs and toads) except Xenopus like mammals. In reptiles
examples of both kinds occur as well as temperature determination of sex in certain turtles and
crocodilians.

Among the arthropods similar differences prevail. Diptera generally have heterogametic males
while Lepidoptera are like birds and urodeles with heterogametic females. In the social insects a
haplo-diplo (male-female) system operates. In certain parasitic forms even the size of the host can
determine the sex of the parasite. The literature is well reviewed in Bull's (BULL 1983) book
significantly titled "Evolution of Sex Determining Mechanisms". The Russian cytologist N. N.
Vorontsov was one of the first to call attention to the nonhomology of the various sex determining
devices.

"Just as the transition from isogamy to anisogamy and to oogamy took place independently of each
other in the various phyla of plants so the formation of mechanisms of the cytogenetical sex
determination with differentiated heterochromosomes follows the same pattern in various kingdoms
and phyla and results in an independent occurrence of the XX-XY system in Melandrium as well
as in many Insecta and Mammalia, whereas the ZW-ZZ system evolved independently in
Trichoptera, Lepidoptera, Serpentes and in Aves. Against the background of these facts it is unclear
whether the male species of different groups are homologous to each other or not; they appear to be
nonhomologous" (VORONTSOV 1973).

This remarkable conclusion is of course totally incompatible with the neo-Darwinian concept of the
evolutionary process.

It is again useful to recall the historical literature. August Weismann
(WEISMANN 1891) was one of Darwin's most ardent supporters and was
instrumental in ridding Darwinism of its Lamarckian elements, leading to
what we now regard as neo-Darwinism. He popularized the idea of the
continuity of the germ plasm with all heritable changes originating in the
reproductive cells. The notion of the continuity of the germ cells seems
so reasonable that it might never occur to someone that it might not be
so, yet that is exactly what a large body of experimental and descriptive
literature clearly discloses.

I have discussed this evidence elsewhere (DAVISON 1984) and will simply summarize the salient
features for the purpose of the present argument.

The vertebrate gonad develops from portions of the urogenital ridge, a bipartite structure consisting
of an outer cortex and inner medulla. The gonadal cortex develops into the ovary, the medulla into
the testis. Oddly the vertebrate gonad is a sterile organ completely incapable of functioning as a
germinal epithelium (NIEUWKOOP and SUTASURYA 1979). During embryonic development the
gonad receives, by a process of invasion, presumptive germ cells from extra-gonadal sources.
Gonads failing to receive these cells remain sterile, while those receiving presumptive germ cells
differentiate with the sex of the host organ not that of the donor cells. Thus the gonad proper is
clearly a part of what Weismann called the somatoplasm.

The important point to make here is that the sources as well as the means of induction and modes
of reaching the gonad vary in nonhomologous fashion from vertebrate group to group in a manner
which remarkably parallels the equally nonhomologous modes of sex determination.

In mammals, including man, the presumptive germ cells are first seen in the region of the allantois
corresponding roughly to the position of the urinary bladder in the adult. From here they migrate
anteriorly and laterally to enter the embryonic gonad. In birds the future germ cells originate outside
the embryonic axis in the extra-embryonic endoderm consisting of the so-called germinal crescent
anterior and lateral to the head. From here they enter the vitelline circulation and after a period in
the circulatory system invade the gonad after first passing through the walls of the venous
circulation. Reptiles as one might expect show a similarity with variations on the bird mechanism.
It is in the amphibia that the most dramatic differences are manifest in the origin of the germ cells.
From their monograph Nieuwkoop and Sutasurya write:

"When comparing PGC formation in the urodeles with that in the anurans, one is unavoidably led
to the conclusion that not only do the PGCs originate from two different sites in the two groups, but
that there are moreover two fundamentally different mechanisms at work ... In the anurans all the
PGCs originate from the endodermal moiety of the egg in the vicinity of the vegetal pole, whereas
in the urodeles they arise from the animal 'ectodermal' moiety, more particularly the presumptive
lateral plate mesoderm in the ventral to ventro-lateral equatorial region. In the anurans all the
descriptive and experimental evidence pleads in favor of the predetermined nature of the PGCs,
based on the presence of a germ-cell-specific sytoplasmic component, the germinal plasm, which
is present in the embryo from the very beginning of development. In constrast, in the urodeles the
PGCs develop strictly epigenetically from common, totipotent cells of the animal moiety under the
inductive influence of the ventral yolk endoderm" (NIEUWKOOP and SUTASURYA 1979).

Note the clear correlations between nonhomologous modes of sex determination and equally
nonhomologous methods and sources for germ cell formation. As I have indicated elsewhere any
theory of evolution must include in its postulates these fundamental differences (DAVISON 1984).
As well as I can determine the neo-Lamarckians, the neo-Darwinians, and the Creationists all fail
even to acknowledge the existence of this experimental and descriptive literature, not to mention its
significance for their particular views. In that respect the Creationists are missing an opportunity
for their case since nonhomology means separate origin, which primafacie might be interpreted to
mean special creation.

First, since the definitive sex cells of the various vertebrate groups cannot be homologized, they
cannot be considered as ancestral cell lineages. Rather they are secondary or derived lineages
correlated in their origins with the equally independent and nonhomologous invention of sexual
reproduction.

We may never know the original source of the reproductive cells but it may have been the gonad
itself, since in the most primitive of the chordates, the tunicates and the cephalochordates
(Amphioxus) the gonad apparently does still function as a germinal ephithelium (NIEUWKOOP and
SUTASURYA 1979).

Secondly, if the original source has been replaced, it seems reasonable that three phases may be
postulated for the evolutionary scenario.

The first phase would be the pre-sexual phase employing the original and common source of
reproductive cells, with these possibly derived from the gonad proper. I have suggested earlier that
this form of pre-sexual reproduction could be a form cytogenetically the same as the first meiotic
division. It should be recalled that the first meiotic division represents a perfectly valid form of
diploid reproduction in its own right, and has intrinsic in its chromosomal mechanism the capacity
to produce from single chromosomal rearrangements those rearrangements as paired homozygotes
in a single step, at the same time that it retains the original karyotype (DAVISON 1984). This is due
of course to the universal property of the first meiotic division that the sister strands remain
together. Such a cytogenetic system can go a long way toward explaining the absence of
intermediate forms in the fossil record, since the original karyotype can go on producing gene
rearrangements until a trial balloon suddenly results in a saltational evolutionary event. This phase
would of course be exclusively female (gynogenetic) and as such would have a reproductive
efficiency twice that of a typical sexual system. In a primitive world in which new niches are as yet
unoccupied such a mode might be ideally suited for the implementation of major evolutionary
inventions such as hair, feathers, cleiodic eggs and other structural elements for which intermediates
are extremely difficult to imagine. In addition to retaining the original wild type, the semi-meiotic
model also serves to eliminate from the germinal line deleterious genes and gene arrangements
since, except for crossing-over, these would be also expressed immediately as paired homozygotes
(DAVISON 1987).

With the introduction of the extra-gonadal and sexual cell lineage, it seems to me that the two cell
lineages would co-exist during the second phase of the evolutionary process. This phase would
correspond to the explosive phases of mammalian and avian evolution already described by Huxley
and Broom. The competition between the two reproductive devices could lead as it apparently has
to the elimination of the primary semi-meiotic device, perhaps due simply to the capacity of the
familiar sexual reproductive mode to fine-tune the genetic makeup to a relatively unchanging
environment.

Viewed in this way the role of sexual reproduction becomes one of evolutionary conservatism rather
than evolutionary creativity, a function which serves to prevent rather than promote progressive
change. Also, unlike the semi-meiotic model, sexual reproduction is not well suited to the
elimination of deleterious genes and gene arrangements. The accumulation of such deleterious
factors coupled with an innate inability to respond effectively to a rapidly changing environment
may have been, in both past and present, important reasons for the extinctions which have
characterized the record of life on the earth.

Also, if this interpretation is essentially correct, we should not be so quick to condemn Lamarckian
evolution, since the properties of the original reproductive lineage are of course completely
unknown. It is perfectly conceivable that those cells could respond to environmental agencies,
which could serve as another reason for their elimination once a new adaptive plateau had been
reached.

When the semi-meiotic hypothesis was first proposed (DAVISON 1984) I pointed out that it has yet
to be demonstrated that any creature reproducing by obligatory sexual means is capable of evolution
beyond the generic level. No response to that challenge has been forthcoming and so I repeat the
proposition. I hope the present paper will serve to stimulate a lively response from the community
of evolutionists.